IEEE Std C57.12.70-2020 pdf download

IEEE Std C57.12.70-2020 pdf download.IEEE Standard for Standard Terminal Markings and Connections for Distribution and Power Transformers.
7.1 Relation between highest voltage winding and other windings
7.1.1 Phase sequence markings
The markings shall be so applied that if the phase sequence of voltage on the highest voltage winding is in the time order H1, H2, H3, it shall be in the time order of X1, X2, X3, and Y1, Y2, Y3, etc. on the other windings.
7.1.2 Phase relationship markings
In order that the markings of terminals shall indicate definite phase relations, they shall be made in accordance with one of the three-phase groups shown in Figure 14. The angular displacement between the H winding and the X winding is the angle in each of the voltage phasor diagrams (see Figure 14), between the lines passing from its neutral point through H1 and Xi, respectively.
7.1.3 Phasor group designation for three-phase transformers
The phasor grouping of a wye, delta or zigzag connected three-phase transformer shall be indicated by the uppercase letters Y, D, or Z for the high-voltage windings and lower case letter of y, d, or z for the low or intermediate voltage windings. The phasor grouping shall be listed from high voltage to low voltage. If a neutral point is externally available, the phasor grouping for the voltage set shall end with an uppercase N or lowercase n as appropriate for the winding voltage level. For an auto connected transformer, the symbol of the lower voltage winding is replaced with the letter ‘ha” for auto. If a transformer is specified with a reconfigurable winding connection (as either dual voltage or dual phase displacement) then the initial connection for service shall be the main phasor group. with the alternative connection (voltage andJor phase displacement) noted in parenthesis.
The phasor grouping can be further described by designating the angular displacement. The angular displacement of a polyphase transformer is the phase angle expressed in degrees between the line-to-neutral voltage of the reference identified high-voltage terminal H1 and the line-to-neutral voltage of the corresponding identified low-voltage terminal X1. The angular displacement may be from 00 to 330° in steps of 30°. The angular displacement number refers to the phase angle, as viewed on a 12 hour clock. For example, one o’clock is 300, two o’clock is 60°, etc. This is sometimes referred to as “clock number notation”, and is intended to be the same format as used in IEC 60076-1. The phasor group designation (sometimes referred to as “vector group”) is the combination of the phasor grouping and the angular displacement.
Many transformer product standards specify that the angular displacement between high-voltage and low- voltage phase voltages of three-phase transformers with A-A or Y-Y connections shall be zero degrees as shown in Figure 14, Group 1. The corresponding phasor group designation would be DdO or YyO, respectively.
If the angular displacement between high-voltage and low-voltage phase voltages of three-phase transformers with A-Y or Y-A connections shall be 30°, with the low voltage lagging the high voltage as shown in Hgure 14, Group 2, then the corresponding phasor group designation would be Dy1 or Yd1, respectively.
7.2 Phase relationships and terminal markings
Phase relationships and terminal markings for distribution transformers shall be as specified in general and product standards IEEE Std C57.12.O0. IEEE Std C57.12.20, IEEE Std C57.12.24, IEEE Std C57.12.34, IEEE Std C57.12.38, and IEEE Std C57.l2.40.
Phase relationships and terminal markings for power transformers shall he as specified in general and product standards IEEE Std C57. 12.00 and IEEE Std C57. 12.10.
Phase relationships and terminal markings for dry-type distribution and power transformers shall be as specified in general and product standards IEEE Std C57.12.O1, ANSI C57.12.50, IEEE Std C57.12.51, and IEEE Std C57.12.52.
73 Marking of full winding terminals
7.3.1 General
The three leads for each winding that connect to the full-phase windings of a three-phase transformer shall have their terminals marked H1, H2, H3, X1, X2, X3, Yi, Y2, Y3, etc. respectively.
7.3.2 Autotransformers
Three-phase autotransformer terminals shall be marked in accordance with the requirements for corresponding multiwinding transformers. (See Figure I 5, Group 3.).